Mechanical vibrating element



June 1934- s. A. SCHELKUNOFF 1,963,719

MECHANICAL VIBRATING ELEMENT Filed March 18, 1931 FIG.

INVENTOR S. A. SCHEL/(UNOFF ATTORNEY Patented June 19, 1934 staresrArsnr creme.

to Bell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Application March 18, 1931,Serial No. 523,459 Claims. (01. 84-402) stant frequency the mostsatisfactory system has which uses the vibrations to control theelectrical the electrical been found to be one of a mechanical elementwave, a portion of the energy in system being fed back to the mechanicalelement system has energy mechanical vibrating to cause it to continuevibrating at its resonant frequency. In such systems a tuning fork, orV-shaped bar, has been largely used. Such a losses due to thelongitudinal motion of the fork as a whole, and also due to thediscontinuity of medium at its ends. It is an unbalanced vibratingsystem. A tuning fork cannot be supported without damping, as it has notrue nodes.

The object of this invention is to provide a element which will be freefrom the above objectionable characteristics.

A mechanical vibrating element built in the shape of a circular ring hasperfect symmetry so that there are no losses due to discontinuity ofmedium, but it cannot serve as a mechanical vibrator because it has notrue nodes; that is, the nodes with respect to radial motion areantinodes with respect to peripheral motion.

My invention consists in a relatively narrow oval ring, which overcomesboth of the above objections. Such an oval ring is symmetrical and,therefore, balanced. There are no energy losses due to movement of thering as a whole, as in the case of a tuning fork or V-shaped bar. Thereis no discontinuity of medium at the end, and hence no reflectionlosses. There are true nodes near each end so that it can be supportedwithout damping.

In the drawing, Fig. 1 is an elevation of a mechanical vibrating elementof rectangular crosssection, in the shape of a narrow oval ring,

Fig. 2 is an elevation of a mounting for such a tuning fork, and

Fig. 3 is a sketch showing how the nodes may be found.

It is desirable for the element to be of rectangular cross-sectionbecause of the mechanical simplicity of such a design, and the resultingassurance that the manufactured article will have perfect balance.

For the same reasons the curved portions at the ends of the oval ringare shaped to be semicircular. This is an important feature, as theseportions are particularly difficult to make with perfect symmetry, andany lack of symmetry introduces energy losses, changes the frequency,and tends to cause variations in the frequency with use.

A mechanical vibrating element of the type illustrated by Fig. 1 hasbeen operated as in accordance with the present disclosure and found tohave the attributes there described. Such mechanical element had thefollowing dimensions: Length 24 /2 inches; outside width 1 inches; widthof the prongs, that is, the dimension in 5 the direction of the width ofthe element as a whole, inch; and depth of the prongs /8 inch.

As shown in Fig. 2 a rigid supporting member 2 has securely fastenedthereto four pins 3 which engage the vibrating element 1 at the twonodal points at one end of the fork. The fork is preferably mountedhorizontally, with a similar supporting member at the other end,although obviously there are several alternatives, the essentialcondition being a nodal point mounting.

In Fig. 3 there is illustrated a method of determining the nodal points.If a line 6 is drawn across the vibrating element, perpendicular to thestraight portion, through the points joining the straight portion withthe semi-circular curved portion, and lines '7, 8 are drawn as shown,making 45 angles with line 6, the nodes will lie within the shadedportions 4, 5 thus determined. The nodes will usually be closer to thelines "I, 8 than 5 to line 6. The exact location of the nodes may befound by experiment, since clamping at such nodal points will give thesmallest decrement to the fork.

Very small depressions may usually be provided at the nodal pointswithout harmful effect on the characteristics of the fork. This willpermit the mounting to be more rigid, and will also permit the fork tobe mounted more quickly and easily a second time if it is necessary toremove it from its original mounting.

An illustration of how a vibrating element may be controlled to produceelectric waves of constant frequency may be found in United StatesPatent 1,560,056, issued November 3, 1925, to J. W. Horton, in which atuning fork is set into vibration, and an electromotive force is inducedin a coil adjacent thereto. The electromotive force is impressed on avacuum tube amplifier, and a part of the output current is used to drivethe fo'rk by means of a second coil.

The vibrating element may also be used as a selective filter in a mannersimilar to that shown in United States Patent 1,708,945, issued April16,

which a wave is km 1929, to J. W. Horton, 1n

' pressed on a fork by means of a coil, and the filtered wave is takenoff by means of a second coil. The vibrating element suppresses allfrequencies other than the resonant frequency of the fork.

What is claimed is:

1. A resonantly vibratory mechanical element n the shape of a relativelynarrow oval ring.

2. An elastically vibratory mechanical element shaped like an elongatedclosed loop which is symmetrical about a system of three mutuallyright-angularly related axes.

3. An elastically vibratory mechanical element

